The investigational agent, T-20, is a 36-amino acid synthetic peptide. T-20 is a linear molecule composed of naturally-occurring 1-amino acid residues. The results of in vitro infectivity assays indicate that T-20 possesses potent and selective anti-HIV activity. T-20 demonstrates antiviral potency in the ng/ml range against viral infectivity and cell to cell fusion for prototypic and primary virus isolates in continuous T-cell lines, freshly-isolated peripheral blood mononuclear cells, macrophages, and in CD4 negative cell lines. Biophysical studies indicate that T-20 demonstrates a specific high- affinity association for a primary sequence motif within the gp41 (envelope) protein product of HIV-1. The purpose of this study is to evaluate the safety, pharmacokinetic profile, and relative antiretroviral activity of T-20 when administered as single and multiple intraavenous doses in HIV infected patients.